Microelectronic package with terminals on dielectric mass

ABSTRACT

A package for a microelectronic element  48 , such as a semiconductor chip, has a dielectric mass  86  overlying the package substrate  56  and microelectronic element  48  and has top terminals  38  exposed at the top surface  94  of the dielectric mass  86 . Traces  36   a,    36   b  extending along edge surfaces  96, 108  of the dielectric mass  86  desirably connect the top terminals  38  to bottom terminals  64  on the package substrate  56 . The dielectric mass  86  can be formed, for example, by molding or by application of a conformal layer  505.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national phase entry under 35 U.S.C. §371 of International Application No. PCT/US2011/060551 filed Nov. 14, 2011, which claims priority from Korean Patent Application No. 10-2010-0113271 filed Nov. 15, 2010, all of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to microelectronic packaging.

BACKGROUND OF THE INVENTION

Microelectronic elements such as semiconductor chips commonly are provided with elements which protect the microelectronic element and facilitate its connection to other elements of a larger circuit. For example, a semiconductor chip typically is provided as a small, flat element having oppositely facing front and rear surfaces and contacts exposed at the front surface. The contacts are electrically connected to the numerous electronic circuit elements formed integrally within the chip. Such a chip most commonly is provided in a package having a miniature circuit panel referred to as a package substrate. The chip is typically mounted to the package substrate with the front or rear surface overlying a surface of the package substrate, and the package substrate typically has terminals exposed at a surface of the substrate. The terminals are electrically connected to the contacts of the chip. The package typically also includes some form of covering overlying the chip on the side of the chip opposite from the package substrate. The covering serves to protect the chip and, in some cases, the connections between the chip and the conductive elements of the package substrate. Such a packaged chip can be mounted to a circuit panel such as a circuit board by connecting the terminals of the package substrate to conductive elements such as contact pads on the larger circuit panel.

In certain packages, the chip is mounted with its front or back surface overlying an upper surface of the package substrate, whereas terminals are provided on the oppositely facing lower surface. A mass of a dielectric material overlies the chip and, most typically, the electrical connections between the chip and the conductive elements of the package substrate. The dielectric mass can be formed by molding a flowable dielectric composition around the chip so that the dielectric composition covers the chip and all or part of the top surface of the package substrate. Such a package is commonly referred to as an “overmolded” package, and the mass of dielectric material is referred to as the “overmold.” Overmolded packages are economical to manufacture and thus are widely used.

In some applications, it is desirable to stack chip packages on top of one another, so that plural chips can be provided in the same space on the surface of the larger circuit panel. Certain overmolded packages incorporate stacking contacts exposed at the top surface of the package substrate outside of the area covered by the chip and, typically, outside of the area covered by the overmold. Such packages can be stacked one atop the other with interconnecting elements such as solder balls or other conductive connections extending between the stacking contacts of the lower package and the terminals of the next higher package in the stack. In such an arrangement, all of the packages in the stack are electrically connected to the terminals on package at the bottom of the stack. In such an arrangement, however, all of the interconnecting elements must be accommodated in the limited region of the package substrate outside of the area covered by the overmold. Moreover, because the package substrate of the higher package in the stack sits above the dielectric overmold in the next lower package, there is an appreciable gap in the vertical direction between the terminals of the higher package and the stacking contacts of the lower package. The interconnecting elements must bridge this gap. This typically requires interconnecting elements spaced at relatively large intervals. Therefore, the number of interconnecting elements which can be accommodated using package substrate of a given size is limited.

Despite the considerable effort devoted in the art to development of stackable packages and other packages having top-surface mounting pads, further improvement would be desirable.

BRIEF SUMMARY OF THE INVENTION

One aspect of the invention provides a microelectronic package. A package according to this aspect of the invention desirably includes a first microelectronic element as well as a package substrate having upper and lower surfaces extending in horizontal directions and edges extending between the upper and lower surfaces. Desirably, the package substrate has electrically conductive elements including bottom terminals exposed at the lower surface of the package substrate. The microelectronic element preferably is disposed over the upper surface of the package substrate and connected to at least some of the conductive elements on the package substrate. The package according to this aspect of the invention preferably includes a dielectric mass covering the microelectronic element and at least part of the upper surface of the package substrate. The dielectric mass defines a top surface remote from the package substrate facing away from the package substrate. Preferably, at least a part of the top surface extends over the microelectronic element. The dielectric mass desirably also defines a first edge surface extending downwardly from a top border adjacent the top surface of the dielectric mass to a bottom border adjacent the package substrate, the bottom border being disposed inside the edges of the package substrate. Preferably, the dielectric mass further defines an upwardly-facing first flange surface extending away from the bottom border of the first edge surface in a horizontal direction adjacent the package substrate, the first flange surface being disposed at a vertical distance from the package substrate less than a vertical distance between the package substrate and the top surface.

Most preferably, the package includes a plurality of top terminals exposed at the top surface of the dielectric mass and a plurality of first traces extending from the top terminals along the top surface and extending along the first edge surface, the first traces having bottom portions adjacent the package substrate extending along the flange surface, the bottom portions being electrically connected to the conductive elements of the package substrate.

As further discussed below, certain packages according to this aspect of the invention can provide numerous top terminals connected to numerous conductive elements on the package substrate. These packages can be used, for example, in a stacked arrangement wherein the top terminals of one package are connected to the bottom terminals of another package.

A package according to a further aspect of the invention desirably includes a microelectronic element and a package substrate having upper and lower surfaces extending in horizontal directions, the microelectronic element being disposed over the upper surface of the package substrate. Desirably, the microelectronic element is electrically connected to at least some conductive elements on the package substrate. The package according to this aspect of the invention desirably includes an overmold covering the microelectronic element and at least part of the upper surface of the microelectronic element, the overmold defining a top surface remote from the package substrate facing away from the package substrate, at least a part of the overmold top surface extending over the microelectronic element. The package desirably further includes top terminals exposed at the top surface of the overmold; and a plurality of traces extending from the top terminals along the top surface of the overmold, the top terminals and traces being embedded in the overmold. Most preferably, the traces are solid metal traces.

Further aspects of the invention provide systems which incorporate packages according to the foregoing aspects of the invention in conjunction with other electronic devices. For example, the system may be disposed in a single housing, which may be a portable housing.

Still further aspects of the invention provide methods of making microelectronic packages. One such method includes steps of a positioning a carrier such as a sheet bearing a plurality of traces over an assemblage of a package substrate with conductive elements and a microelectronic element overlying the package substrate and electrically connected to the conductive elements, the positioning step being conducted so that portions of at least some of the traces extend over the microelectronic element. The method desirably also includes the step of introducing a flowable composition between the carrier and the package substrate and around the microelectronic element and curing the composition to form an overmold covering the microelectronic element and having a shape at least partially defined by the carrier. Preferably, the method also includes removing the carrier so as to leave the traces extending over one or more surfaces of the overmold facing away from the package substrate.

A further method according to this aspect of the invention desirably includes the step of positioning a carrier such as a sheet bearing a plurality of traces over an assemblage of a package substrate with conductive elements and a microelectronic element overlying the package substrate and electrically connected to the conductive elements. In this method, the positioning step desirably is performed so that a first portion of the carrier and first portions of the traces on the first portion of the carrier extend over the microelectronic element and a second portion of the carrier and second portions of the traces on the second portion of the carrier extend from the first portion toward the package substrate. For example, the carrier may be a sheet with traces thereon, and the sheet may be bent or otherwise deformed so that the second portion of the carrier projects from the first portion of the carrier toward the package substrate.

This method desirably also includes the steps of introducing a flowable composition between the sheet and the package substrate and around the microelectronic element and curing the composition to form an overmold covering the microelectronic element and having a shape at least partially defined by the carrier. Most preferably, the method includes electrically connecting the second portions of the traces with the conductive elements of the package substrate. The connecting step can be performed before or after the overmold is formed. In either case, the proximity of the second portions of the traces to the package substrate facilitates formation of small connections, which in turn helps to provide numerous traces in a package of limited size.

A further method of making a microelectronic package includes the step depositing a conformal dielectric layer onto an assemblage of a package substrate with conductive elements including bottom terminals exposed at a lower surface of the package substrate and a microelectronic element overlying an upper surface of the package substrate and electrically connected to the conductive elements. Desirably, the depositing step is performed so that a first portion of the conformal layer defines a top surface remote from the package substrate and extending over the microelectronic element and one or more additional portions of the conformal layer define one or more edge surfaces extending downwardly toward the package substrate outside of an area covered by the microelectronic element. The method desirably includes providing traces and top terminals on the conformal layer so that the traces extend along the top surface and extend toward the package substrate along at least one edge surface and bottom portions of the traces are positioned adjacent the package substrate. Desirably, the method further includes connecting the bottom portions of the traces to at least some of the conductive elements on the package substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic bottom plan view of a component used in a method of manufacturing a package according to one embodiment of the invention.

FIG. 2 is a diagrammatic elevational view of the component depicted in FIG. 1.

FIG. 3 is a diagrammatic sectional view depicting a manufacturing step using the component of FIGS. 1 and 2.

FIG. 4 is a diagrammatic sectional view similar to FIG. 3, but depicting the component and associated elements at a later stage in the manufacturing process.

FIG. 5 is a diagrammatic sectional view similar to FIGS. 3 and 4, depicting the component and associated elements at a later stage in the manufacturing operation.

FIG. 6 is a view similar to FIGS. 3-5, but depicting a still later stage in manufacture.

FIG. 7 is a diagrammatic top plan view depicting the package made using the manufacturing process of FIGS. 3-6.

FIG. 8 is a fragmentary sectional view on an enlarged scale taking along line 8-8 in FIG. 7.

FIG. 9 is a diagrammatic sectional view of the package depicted in FIG. 7 in conjunction with another package.

FIG. 10A is a fragmentary sectional view on an enlarged scale showing a portion of the package of FIG. 9.

FIG. 10B is a fragmentary sectional view depicting a portion of a package in accordance with a further embodiment of the invention.

FIG. 11 is a fragmentary sectional view depicting a portion of a manufacturing process according to a further embodiment of the invention.

FIG. 12 is a fragmentary sectional view depicting a portion of the package made in the process of FIG. 11.

FIG. 13 is a fragmentary sectional view depicting a stage in a manufacturing process according to yet another embodiment of the invention.

FIG. 14 is a fragmentary sectional view depicting a portion of the package made using the process of FIG. 13.

FIG. 15 is a fragmentary sectional view depicting a stage in a manufacturing process according to yet another embodiment of the invention.

FIG. 16 is a fragmentary sectional view depicting a portion of the package made in the process of FIG. 15.

FIG. 17 is a diagrammatic sectional view depicting a stage in manufacturing process according to yet another embodiment of the invention.

FIG. 18 is a sectional view depicting the package made in the process of FIG. 17.

FIG. 19 is diagrammatic sectional view of a package according to yet another embodiment of the invention.

FIG. 20 is a diagrammatic sectional view of a package according to a further embodiment of the invention.

FIG. 21 is a diagrammatic sectional view depicting a package according to yet another embodiment of the invention.

FIG. 22 is a diagrammatic view depicting a system according to one embodiment of the invention.

DETAILED DESCRIPTION

A component utilized in a manufacturing process according to one embodiment of the invention incorporates a carrier in the form of a metallic sheet 30 as, for example, a sheet of copper (FIGS. 1 and 2) having a first surface 32 and an opposite second surface 34. The first surface 32 bears a plurality of electrically conductive traces 36. The traces are formed as elongated strips of a conductive material, preferably a solid metal such as copper, gold, nickel, and combinations thereof on the first surface 32 of sheet 30. The traces are formed integrally with terminals 38 of similar composition. The terminals are disposed in a first portion 40 of the sheet, schematically indicated by a broken line. The traces extend from the terminals into a second portion 42. In this embodiment, second portion 42 includes regions on opposite sides of the first portion 40. Although only a few terminals 38 and a few traces 36 are depicted in FIGS. 1 and 2, in practice, there can be hundreds or more terminals and traces.

Terminals 38 are disposed in an “area array” within first portion 40. As used in this disclosure, the term “area array” means an array of terminals in which the terminals are substantially dispersed over a two-dimensional region, rather than concentrated in a few rows such as rows only at the perimeter of the region or rows only in the center of the region. Although the particular area array shown in FIG. 1 is a rectilinear, uniform array, this is not essential.

The terminals and traces can be fabricated by numerous known metal working methods as, for example, by etching a sheet originally having a thickness greater than sheet 30 so as to remove metal from areas other than those occupied by the terminals and traces, or by plating the terminals and traces onto the sheet. FIGS. 1 and 2 depict only a single sheet of a size suitable for making a single package. In practice, however, the sheet desirably is provided as a continuous or semi-continuous element incorporating numerous portions, each such portion constituting the sheet shown in FIGS. 1 and 2, these portions being continuous with one another.

The sheet according to FIGS. 1 and 2 is utilized in conjunction with an assemblage 46 (FIG. 3) incorporating a microelectronic element 48 such as a semiconductor chip having a front surface 50, a rear surface 52, and contacts 54 exposed at the front surface. Assemblage 46 also includes a package substrate in the form of a small circuit panel incorporating a generally planar dielectric structure 56 having a top surface 58 and an oppositely facing bottom surface 60. The words “top” and “bottom” as used herein refer to the frame of reference of the elements discussed and do not refer to the normal gravitational frame of reference. Package substrate 56 also includes conductive elements which, in this instance, incorporate traces 62 extending on the bottom surface 60 and terminals 64 also exposed at the bottom surface of the dielectric structure and connected to traces 62.

The assemblage also includes wire bonds 66 connecting the contacts 54 of chip 48 with traces 62 on the package substrate. The package substrate has apertures 68 arranged so that traces 62 are exposed at the upper surface of the package substrate through apertures 68. In the particular embodiment depicted in FIG. 3, the package substrates of numerous assemblages are provided as a continuous or semi-continuous element such as a strip, tape or sheet. Thus, although there are visible borders between the individual package substrates 56 in FIG. 3 for clarity of illustration, in practice, there may be no discernable borders at this stage of the process. The apertures 68 in the package substrate 46 desirably are fully closed by the traces 62. Likewise, the apertures where wire bonds 66 penetrate to the traces desirably are fully covered by the traces, so that the package substrate is a continuous, impervious sheet.

In a step of the method, the element including numerous carriers or sheets 30 is positioned over the element including numerous assemblages 46 with their package substrates and chips. Each carrier or sheet 30 is positioned so that the first surface 32 bearing traces 36 and terminals 38 faces toward the package substrates. In the embodiment of FIG. 3, the positioning step includes deforming each carrier sheet 30 from the flat condition depicted in FIGS. 1 and 2 to a deformed condition in which the second portion 42 of each sheet is bent out of plane from the first portion 40, with the second portion 42 projecting in the direction of first surface 32 as indicated schematically at 42′ in FIG. 2. This may be done by essentially any conventional forming technology as, for example, by use of a matched metal die in a stamping press. The formed carrier sheets are positioned over the assemblages of chips and package substrates so that the first portion 40 of the carrier sheet 30 (FIG. 1) bearing terminals 38 extends over the microelectronic element or chip 48 and the second portion 42 extends from the first portion 40 toward the package substrate 46.

In this condition, the second portions 42 of the each carrier sheet 30 define sloping regions 70 extending from the first portion 40 of the sheet, and also define flange regions 74 projecting from the sloping regions 70. The traces in the second portions 42 extend along the sloping regions 70 and also extend along the flange regions 74. Thus, those portions of the traces 36 in the second portions 42 of the sheet include slope portions 76 extending along the sloping regions 70 and bottom portions 78 extending on the flange portions 74.

With the carrier sheets 30 positioned over the package substrate 46, the bottom portions 78 of the traces and the flange regions 74 of the sheet are disposed close to the package substrate 46. The bottom portions 78 of the traces on the sheet are connected to the traces 62 on the package substrate by any suitable connection as, for example, by solder bonds 80. The positions of the traces on the carrier sheet 30 and the positions of the conductive features on the package substrate 56 can be controlled with excellent accuracy. This facilitates the bonding process and facilitates the use of small-diameter bonds which allow close spacing of the traces.

After the traces on the carrier sheets have been bonded to the traces on the package substrates, the assembled parts are placed into a mold, so that a first side 82 of the mold supports the carrier sheets 30, whereas a second side 84 of the mold supports the package substrates 46. Although the mold parts are depicted as closely overlying the carrier sheets and package substrates, there is no need for sealing engagement between the mold parts and the carrier sheets 30 or package substrates 46. Rather, the mold parts serve to physically support the carrier sheets and package substrates and prevent distortion of these elements during the molding step discussed below.

In the next step (FIG. 4), a flowable composition as, for example, an epoxy is introduced into the space between each carrier sheet 30 and the associated package substrate 46 and around the chip or microelectronic element 48 on the package substrate. This flowable composition is cured to form an overmold 86 (FIG. 4). As the flowable composition is introduced, it contacts the carrier sheet and thus assumes a shape defined at least partially by the carrier sheet. Also, the flowable composition flows into intimate contact with the traces and terminals and partially surrounds the traces and terminals. However, because the carrier sheet 30 is in intimate contact with the surfaces of the traces and, particularly, the terminals 38, the faces of the terminals facing toward the carrier sheet are fully protected from contact with the flowable composition. Also, the package substrate 46 protects the terminals 64 on the package substrate from contamination by the flowable composition. Because the carrier sheets 30 and package substrates 46 are provided as continuous or semi-continuous sheets, there is no need for the mold parts to confine the flowable composition at the margins of any one particular carrier sheet or package substrate. The flowable composition may be introduced into the space between one carrier sheet and package substrate and may flow into the spaces between other carrier sheets and package substrates.

In the next phase of the process, the mold elements 82 and 84 are removed, leaving the carrier sheets 30 exposed on one side of the molded assemblages and leaving the terminals 64 on the package substrates exposed on the opposite side (FIG. 5). In the next phase of the process, the carrier sheets 30 are removed as, for example, by exposing the carrier sheets to an etchant which is effective to remove the carrier sheet but which leaves the terminals 38 and traces 36 substantially intact. After etching, the assemblages have the configuration illustrated in FIG. 6. The assemblages are then severed along lines of separation 88 to yield individual microelectronic packages 90.

Each package 90 (FIGS. 7-9) includes a package substrate 56 with an upper surface 58 and a lower surface 60 extending in horizontal directions and edges 92 extending between the upper and lower surfaces. The package 90 also has electrically conductive elements including the traces 62 and terminals 64 exposed at the lower surface 60. In the completed package, terminals 64 are referred to as “bottom terminals.” As used herein with reference to a conductive element such as a terminal or trace, the term “exposed at” a surface means that the conductive element is accessible from that surface. In the particular embodiment illustrated, bottom terminals 64 are disposed on the lower surface 60 so that the bottom terminals project slightly from the lower surface. However, the bottom terminals can be exposed at the lower surface, even if the bottom terminals are embedded in the package substrate 56 or disposed on the top surface 58 of the substrate, provided that there are openings in the substrate which allow access.

The package 90 also includes a first microelectronic element 48 in the form of a chip, such microelectronic element being disposed over the upper surface 58 of the package substrate and electrically connected to the conductive elements, particular traces 62 and bottom terminals 64 on the package substrate.

The package further includes a dielectric mass in the form of the overmold 86 formed during the molding process discussed above, such dielectric mass covering the microelectronic element 48 and at least part of the upper surface of the package substrate. The dielectric mass or overmold 86 defines a top surface 94 remote from the package substrate 56. At least a part of the top surface 94 extends over the microelectronic element 48. Mass or overmold 86 also defines a first edge surface 96 extending downwardly from a top border 98 adjacent top surface 94 to a bottom border 100 adjacent the package substrate 56 and disposed inside the edges 92 of the package substrate. That is, bottom border 100 is disposed within the horizontal area bounded by the edges 92 of the package substrate. The first edge surface 96 of the dielectric mass slopes away from the microelectronic element 48 in a first horizontal direction H₁ (FIGS. 7, 9 and 10A), so that the bottom border 100 of the first edge surface is further from the microelectronic element than the top border 98 in the horizontal direction H₁. The first edge surface 96 is shaped such that any straight line extending along the first edge surface at a constant vertical distance from package substrate 56 is disposed at a constant location in the first horizontal direction H₁. For example, an imaginary line 102 (FIG. 7) extending at a constant vertical distance from the package substrate would also lie at a constant horizontal location. In the particular embodiment shown, the first edge surface is substantially planar.

As best seen in FIG. 10A, the dielectric mass or overmold further defines a first flange surface 104 facing upwardly, away from the package substrate 56. The first flange surface extends in the first horizontal direction H₁, away from bottom border 100 of first edge surface 96. The first flange surface 104 is disposed adjacent package substrate 56. The distance D₁ between the first flange surface 104 and the top surface 58 of the package substrate is considerably less than the distance D_(T) between the top surface 94 of the dielectric mass and the top surface 58 of the package substrate.

As shown in FIGS. 7, 9, and 10A, terminals 38 are exposed at the top surface 94 of the dielectric mass. In the completed package, terminals 94 are referred to as “top terminals.” A plurality of traces 36 a extend along top surface 94 from some of the top terminals 38, and further extend across top border 96 and along the first edge surface 96. Those portions of the traces extending along the first edge surface 96 are substantially parallel to one another. The traces include bottom portions 78, which extend along the first flange surface 104. As used in this disclosure, a statement that a trace extends “along” a surface means that the trace extends in proximity to the surface and substantially parallel to the surface. In the particular embodiment depicted in FIGS. 7, 9, and 10A, the traces are embedded in top surface 94, first edge surface 96, and flange surface 104, with the surfaces of the traces lying substantially flush with the surfaces of the dielectric mass or overmold 86. For example, as seen in FIG. 8, the surface of trace 36 a is flush with first edge surface 96. This particular flush disposition results from the fact that the top surface 94, first edge surface 96, and flange surface 104 are formed by the carrier sheet, and the traces were carried on the surface of the carrier sheet at the time of formation. Similarly, top terminals 38 are embedded in the top surface 94 of the dielectric mass. The embedded traces and terminals may be formed from a solid metal as, for example, a solid copper or copper alloy. Typically, a solid metal provides higher conductivity than a composite including metal and a binder. The bottom portions 78 of the traces 36 a reside on the flange surface 104 because the bottom portions originally resided on the flange portion 74 of the sheet (FIG. 3). The bottom portions 78 of the traces, of course, remain connected to the conductive elements of the package substrate, and particularly to traces 62, so that the traces 36 a, and hence some of top terminals 38 are connected to some of the bottom terminals 64 and to microelectronic element 48.

The package further includes a second edge surface 108 extending downwardly from top surface 94 and sloping away from microelectronic element 48 in a second horizontal direction H₂, opposite from the first horizontal direction H₁, and a second flange surface 110 extending from the bottom border of second edge surface 108 in the second horizontal direction. The package further includes traces 36 b extending from some of top terminals 38 along top surface 94, second edge surface 108, and second flange surface 110. These features are identical to the features of the first edge surface 108, first flange surface 104, and traces 36 a discussed above, except that the directions are reversed. Traces 36 b connect some of the top terminals 38 to some of the bottom terminals 64 and to microelectronic element 48 through some of the traces 62 on the package substrate.

In this arrangement, some or all of the top terminals 38 are connected to the contacts 54 of the microelectronic element or chip 48 by way of the conductive elements on the package substrate, and some or all of the top terminals 38 are also connected to some or all of the bottom terminals 64. The top terminals 38 are arranged in a pattern corresponding to those of the bottom terminals 64. Thus, as shown in FIG. 9, two or more of the packages 90 can be superposed in a stack, with the top terminals of the bottom package 90 a in the stack connected to the bottom terminals 64 of the next higher package 90 b. The bottom terminals 64 of the lower-most or bottom package of the stack can be connected to conductive elements such as contact pads 112 on a larger circuit substrate 114, so that the entire stack is mounted and connected to the circuit panel.

A solder mask (not shown) can be applied over the traces 36 extending on the overmold or dielectric mass. Similarly, a solder mask can be provided as needed on the conductive features of the package substrate. Such solder mask can be applied and patterned in any conventional manner. The solder mask serves to limit the spread of solder along the surfaces of the traces.

Of course, the arrangements discussed above with reference to FIGS. 1-10A can be varied in many ways. For example, the conductive features such as the traces 62 are depicted as lying on the bottom surface of the package substrate 56. However, the traces can be disposed on the top surface of the package substrate, or even within the package substrate. Moreover, the package substrate can include more than one layer of traces.

In a further variant, (FIG. 10B) the process discussed above is modified in that the traces on the carrier sheet are not connected to the conductive features of the package substrate prior to introduction of the dielectric composition to form the dielectric mass. Numerous traces 36 a extend along the first edge surface 96′ of the dielectric mass. Traces 36′ are formed with bottom portions 78′ extending along the flange surface 104′ of the dielectric mass, but are not connected to the conductive features such as traces 62′ on the package substrate 56′ before the molding operation. Either before or after removal of the carrier or sheet (not shown), vias 105 are formed through the flange portion 107 of the dielectric mass, i.e., the portion disposed beneath the flange surface 104′. Conductors 109 are disposed within these vias and connect the bottom portions 78′ of the traces to the conductive elements of the dielectric substrate 56′. In the particular embodiment depicted in FIG. 10B, the vias are formed from the bottom surface of the substrate and hence extend through the substrate, as well as through the flange portion 107 of the dielectric mass or overmold, so that the vias reach from the traces 62′ on the bottom surface of the package substrate to the bottom portions 78′ of the traces 36′ on the dielectric mass. Positioning of the bottom portions 78′ of the traces close to the package substrate greatly facilitates formation of vias 109. Stated another way, distance D₁ between the flange surface 104′ is considerably smaller than the distance D_(T) between the package substrate and the top surface. Therefore, the distance which must be penetrated by the vias is much smaller than would be the case if the dielectric mass had a flat top surface extending over the entire package substrate, so that the entire dielectric mass had thickness equal to D_(T). This facilitates formation of relatively small-diameter vias as are necessary to accommodate relatively closely spaced traces.

In other embodiments, the vias 105 need not penetrate through the package substrate. For example, where the conductive elements include traces on the top surface of the package substrate 56′, the vias may be formed from the flange surface and penetrate through only the flange portion 107 of the dielectric mass or overmold.

A process according to a further embodiment of the invention (FIGS. 11 and 12) is similar to the process discussed above, except that the traces 236 and top terminals 238 are carried on a dielectric sheet 230. The dielectric sheet is deformed and positioned over the assemblage of the package substrate 256 and microelectronic element 248 in a manner similar to that discussed above. Thus, a first portion 240 of the carrier and corresponding first portions of traces 236 extend over the microelectronic element, whereas a second portion 242 of the carrier sheet and those portions of the traces 236 lying on the second portion 242 extend from the first portion 240 toward the package substrate 256. Again, a flowable composition is introduced between the sheet and the package substrate and around the microelectronic element and cured, so as to form a dielectric mass or overmold 286 covering the microelectronic element and having a shape defined at least partially by sheet 230. Here again, the mass or overmold includes flange surfaces 204 and flange portions underlying the flange surfaces. Portions 278 of traces 236 overlie the flange portions, and thus are disposed adjacent to the package substrate and at a distance closer to the package substrate than the top terminals 238 and the adjacent portions of the traces. In this embodiment, the bottom portions 278 of the traces are not connected to the conductive features of the package substrate prior to introduction of the dielectric composition. Instead, vias are formed through the flange portions of the mass and through the corresponding portions of sheet 230, and via conductors 209 are formed within these vias to connect the bottom portions 278 of the traces to the conductive elements of the package substrate, such as traces 262.

In this embodiment as well, the processes of handling the sheet and molding the dielectric masses may be performed while the sheets and package substrates remain in the form of a continuous or semi-continuous sheet or tape incorporating elements which form numerous individual packages. The packages can be severed from one another before or after forming the vias and via conductors 209.

The completed package, as depicted in FIG. 12, incorporates portions of sheet 230 as part of the package structure. Desirably, the sheet 230 adheres to the dielectric mass 286. For this purpose, the sheet 230 may incorporate an adhesive at surface 231, which faces toward the package substrate during the molding process. Thus, the dielectric sheet 230 forms a layer closely overlying the dielectric mass 286 and adhering thereto in the final product. In other embodiments, the flowable dielectric material itself may serve as an adhesive which bonds the formed dielectric mass to the sheet. Merely by way of example, the sheet may include materials commonly used in flexible printed circuits as, for example, polyimides and BT resin. Also, a solder mask (not shown) may be applied over the traces on the sheet prior to deforming the sheet, provided that the solder mask can withstand the temperatures and pressures used during the molding process.

A process according to a further embodiment of the invention (FIG. 13) uses a pair of mold elements 382 and 384 to form the dielectric mass 386. In this process, the carrier and traces are not present at the time of molding. The dielectric mass has a configuration similar to those discussed above and again includes flange portions 307 defining flange surfaces 304, as well as a top surface 394 and one or more edge surfaces 396. Here again, the edge surfaces extend from top borders at top surface 394 to bottom borders 398 disposed within the area of the package substrate 356. As discussed above, the edges 394 of the package substrate may be defined after the molding step, when the package substrate 356 is severed from a larger sheet or tape.

After the molding process, a sheet 330 carrying the traces 336 and top terminals 338 is applied over the top surface 394 of the dielectric mass and over the edge surfaces 396 and flange surfaces 304. Here again, bottom portions of the traces are disposed adjacent the package substrate 356, so that vias may be readily formed through the relatively thin flange portions 307 of the dielectric mass or overmold. Via conductors 309 are disposed in the vias and electrically connect the traces 336 on the sheet to the conductive elements 362 of the package substrate. In the particular embodiment depicted in FIG. 14, the sheet 330 is bonded to the dielectric mass by a thin layer of an adhesive 301. Also, the sheet carries a solder mask layer 303.

A process according to a further embodiment uses an assemblage 446 similar to those discussed above, except that the microelectronic element or chip 448 is positioned in a “face-down” orientation relative to the package substrate 456. The package substrate incorporates conductive elements including traces 463 on the upper surface of the package substrate, additional traces 462 on the lower surface of the package substrate, bottom terminals 464 and through conductors 465 connecting upper surface traces 463 with the lower surface traces and bottom terminals. The contacts 454 of the microelectronic element or chip 448 are bonded to the upper surface conductive elements 463 as, for example, by solder bonds. The dielectric mass or overmold 486 is formed using mold elements similar to the mold elements discussed above with reference to FIG. 13 and has a similar configuration. Vias 405 are formed through the flange portion of the dielectric mass, from the upwardly facing flange surface 404 to the upper surface conductive elements 463. Vias 405 may be formed during the molding process as, for example, by bumps or protrusions on the mold which engage the upper surface conductive elements. Alternatively, vias 405 may be formed by processes such as laser ablation, etching, sand-blasting or the like after molding. In a further alternative, vias 463 may be formed in part by features of the mold and in part by post-mold processing. After formation of the dielectric mass or overmold 486 and vias 405, a dielectric sheet 430 carrying traces 436 and top terminals 438 is mounted on the dielectric mass using an adhesive layer (not shown). In this embodiment, sheet 430 carries the traces 436 on the surface of the sheet facing toward the dielectric mass. Thus, terminals 438 are exposed at the top surface 494 of the mass through openings 439 in the sheet. These openings can be formed before or after the sheet 430 is assembled to the overmold. The bottom portions 478 of traces 436 are bonded to the upper surface conductive elements 463 of the package substrate 456 by bonds 409 disposed within vias 404. Merely by way of example, such bonds may be formed by soldering, eutectic bonding thermosonic bonding or the like. The bonding materials may be carried on the traces 436 or may be deposited into the vias. Here again, the proximity of the trace bottom portions 478 to the package substrate facilitates the bonding process and the use of small bonds, which, in turn, permit close spacing of the trace bottom portions. Numerous traces can be accommodated on the structure. A package substrate and microelectronic element of the type shown in FIGS. 15 and 16 can be utilized in the processes and structures discussed above. Also, the dielectric sheet 430 with traces on the side facing toward the package substrate can be used in a process similar to that of FIGS. 11 and 12, where the sheet is placed into the mold and the dielectric mass is shaped by contact with the sheet. In this case, openings 439 desirably are formed after the molding process.

A process according to a further embodiment of the invention (FIGS. 17 and 18) forms a dielectric mass on an assemblage 546, which, like the assemblage discussed above with reference to FIGS. 15 and 16, has a microelectronic element in face-down orientation with the contacts 554 facing toward the package substrate 556, so that the contacts are joined to conductive elements on the package substrate. Here again, the assemblage includes bottom terminals 564 carried on the lower surface of the package substrate 556. The particular assemblage depicted in FIG. 17 includes an underfill 501 disposed within the space between the microelectronic element or chip 548 and the package substrate upper surface. The underfill desirably surrounds the connections 503 between the microelectronic element and the conductive elements of the package substrate.

A conformal dielectric layer 505 having a first surface 507 and a second surface 509 is used in the process. When the conformal layer is applied to the assemblage 546, the conformal layer sags into contact with the upper surface 558 of the package substrate 556, with the exposed surfaces of the microelectronic element 548, and with the underfill 501. Thus, at the time the conformal layer is applied to the assemblage, the conformal layer should have sufficient softness and deformability to conform in this manner. Merely by way of example, the conformal layer may be a “B-stage” or partially cured epoxy composition, which may optionally contain a particulate filler material. After application, the conformal layer may be hardened as, for example, by chemical reaction. As the conformal layer deforms to cover the exposed elements of assemblage 546, a first portion of the conformal layer defines a top surface 594, (FIG. 18) remote from package substrate 556 and extending over microelectronic element 548, whereas additional portions of the conformal layer define edge surfaces 596 extending downwardly toward the package substrate in an area of the package substrate outside of the area covered by microelectronic element 548.

After the conformal layer is applied and cured, traces 536 and top terminals 538 are formed on the cured layer. For example, the entire conformal layer can be plated, masked and selectively etched to form the top terminals and traces. Alternatively, the surface of the conformal layer may be covered with a mask material, and then selectively exposed to laser radiation to cut grooves through the mask. A seed layer can be applied over the mask and into the grooves, whereupon the mask is removed so as to lift off the seed layer everywhere except at the grooves. The surface is then exposed to a plating bath, so that metal is deposited only at the grooves where the seed is present. Any other technique for forming metallic features on a dielectric body can be used. Here again, the top terminals are exposed on the top surface 594 and traces 536 extend from at least some of the top terminals along the top surface 594 and also extend downwardly toward the package surface 556 along edge surfaces 596. In this embodiment as well, bottom portions 578 of the traces are disposed at a distance D₅₇₈ from the package substrate, which is smaller than the distance D₅₉₄ between the package substrate and the top surface 594 and hence smaller than the distance between the package substrate and terminals 538. Here again, the difference in height facilitates connection of the bottom portions to the conductive elements of the package substrate. In the particular embodiment of FIG. 18, the conformal layer forms flange portions 507 defining flange surfaces 504, and the bottom portions 578 of the traces extend along the flange surfaces. The bottom portions are connected to the conductive elements of the substrate by forming vias through the flange portions and depositing via conductors 509 in these vias.

The process of applying a conformal layer, like the other processes discussed above, can be conducted using assemblages which are formed as a large sheet of many assemblages having a common package substrate, using a continuous or semi-continuous conformal layer having traces and terminals for numerous packages. The assemblages are severed from one another after application of the conformal layer.

It should be appreciated that the drawings are not to scale. For example, the vertical dimensions of the microelectronic element 548 and the conformal layer itself are greatly exaggerated for clarity of illustration. In practice, the height or distance D₅₉₄ from the package substrate to the top surface and top terminals may be on the order of a few hundred microns or less, commonly about 400 microns or less, whereas the bottom portions 548 of the traces are disposed at an even smaller height D₅₇₈ above the package substrate. The conformal layer forms the dielectric mass of the package. In this regard, the term “dielectric mass” does not imply any particular minimum thickness or shape.

In a variant of the process discussed above with reference to FIGS. 17 and 18, the conformal layer is applied to the assemblages 546 with traces 536 and top contacts 538 already in place on the conformal layer. For example, the conformal layer itself may include plural sub-layers such as a flexible top layer bearing the top contacts and terminals and a conformal bottom layer such as a B-stage epoxy.

Numerous further variations and combinations of the features discussed above can be utilized. Merely by way of example, the dielectric mass may have one, two, or more than two edge surfaces with traces extending thereon. Also, the package may include more than one microelectronic element. Merely by way of example, the package depicted in FIG. 19 is similar to the package discussed above with reference to FIGS. 1-10A, but incorporates two microelectronic elements 748 in the dielectric mass 786.

A package according to a further embodiment of the invention (FIG. 20) incorporates a microelectronic element 848 and package substrate 856 generally similar to the corresponding elements of the packages discussed above with respect to, e.g., FIGS. 9-10A and 10B. In this embodiment as well, the microelectronic element 848 is electrically connected to conductive elements on package substrate 856 and is covered by a first dielectric mass 886. Here again, this dielectric mass defines a top surface 894 and a first edge surface 896 extending toward the package substrate from top surface 894. The dielectric mass also includes a flange portion 804 projecting outwardly in the first horizontal direction H₁ (to the right in FIG. 20).

In the embodiment of FIG. 20, however, substrate 856 extends beyond flange portion 804. An auxiliary dielectric mass 847 is disposed on this protruding portion of the package substrate. Auxiliary dielectric mass 847 defines a top surface 897 coplanar with the top surface 894 of the first dielectric mass 886. The auxiliary dielectric mass also defines an edge surface 895 extending downwardly from the top surface 897 toward the package substrate. Edge surface 895 slopes in the second horizontal direction H₂, opposite to the first horizontal direction, so that the first edge surface 896 of the first dielectric mass 886 and the edge surface 895 of auxiliary dielectric mass 897 converge with one another in the downward direction, toward package substrate 856. These edge surfaces cooperatively define a trench extending downwardly from top surfaces 894 and 897. The trench and edge surfaces are elongated structures extending into and out of the plane of the drawing as seen in FIG. 20. The auxiliary dielectric mass 897 defines a flange region 803 projecting inwardly toward microelectronic element 848 from the bottom border of edge surface 895. Flange region 803 merges with the flange region 804 of the first dielectric mass 886. It should be appreciated that although these dielectric masses and portions are described separately, they are, in fact, portions of a unitary dielectric body.

As in the embodiments discussed above, top terminals 838 are exposed at the top surface 894 of the first dielectric mass 886. Traces 836, connected to at least some of the top terminals, extend along the first edge surface 896 of mass 886 and have bottom portions connected to conductive elements of the package substrate. In the embodiment of FIG. 20, however, auxiliary top terminals 837 are exposed at the top surface 897 of the auxiliary dielectric mass 847. Traces 833 extend from at least some of these auxiliary top terminals along the top surface 897 of the auxiliary mass and along the sloping edge surface 895 of the auxiliary mass 847. Bottom portions of traces 833, disposed adjacent the package substrate 856, are also connected to the conductive elements of the package substrate. As in the embodiments discussed above, the package substrate defines an array of bottom terminals in alignment with the first dielectric mass 886 and in alignment with the top terminals 838 carried by the first dielectric mass. In the embodiment of FIG. 20, the package substrate also defines auxiliary bottom terminals 857 in alignment with the auxiliary top terminals 837, carried on the auxiliary mass 847.

In this embodiment, the first dielectric mass 886 also has a second edge surface 808 sloping in the second horizontal direction H₂, and some of the traces 836 extend from some of the top terminals 838 along the second edge surface 808. The dielectric body includes a second auxiliary mass 809 having auxiliary top terminals 811 exposed at the top surface of this mass, and having an edge surface 813 extending downwardly from the top surface of the mass and sloping in the first horizontal direction H₁, so that edge surface 813 converges with the second edge surface 808 of the first dielectric mass 886. These edge surfaces cooperatively define a further elongated trench extending into and out of the plane of the drawing as seen in FIG. 20. Additional auxiliary traces 815 extend along the edge surface of the additional auxiliary mass 809. These traces are connected to the conductive elements of the package substrate 856. The package substrate defines additional auxiliary bottom terminals 817 in alignment with the additional auxiliary top terminals 811. Auxiliary mass 809 defines a flange region which merges with the flange region at the bottom of second edge surface 808 of the first dielectric mass 886. Here again, the additional auxiliary mass 808 and the first dielectric mass 886 form parts of a unitary dielectric body.

Each of the auxiliary dielectric masses may carry one row or more than one row of top contacts 811, 837. These top contacts and the auxiliary bottom contacts 857, 817, aligned with these top contacts, provide additional connectivity and additional routing of signals in a stack of packages. The packages as shown in FIG. 20 can be stacked one atop the other, with the auxiliary top contacts aligned with the auxiliary bottom contacts of the next higher package in the stack. The top contacts 838 of the first dielectric mass are aligned with the bottom contacts 864 of the next higher package in the stack.

Packages as depicted in FIG. 20 may be fabricated by methods essentially the same as those discussed above and may incorporate the features discussed above. Merely by way of example, the sheet or carrier used to form the package is not present in the finished package depicted in FIG. 21. However, a package with auxiliary dielectric masses can incorporate features such as a dielectric sheet as discussed with reference to FIGS. 11, 12, and 16. In yet another variant, one or more microelectronic elements can be disposed within one or more of the auxiliary masses.

A package according to a further embodiment of the present invention (FIG. 21) is similar to the package of FIG. 20 in that the package of FIG. 21 includes a first or main dielectric mass 686 having a first edge surface 696 and a second edge surface 608. The package further includes a first auxiliary dielectric mass 647 having a sloping edge surface 695 converging with the first edge surface 696 of mass 686, and a second auxiliary dielectric mass having a sloping edge surface 613 converging with the second edge surface 608 of mass 686. Here again, auxiliary top contacts 637 and 611 are provided on the auxiliary dielectric masses, and auxiliary bottom contacts 617 and 657 are provided on the bottom surface of the package substrate for increased connectivity. However, the dielectric masses in the package of FIG. 21 do not include flange surfaces. Thus, edge surfaces 696, 608, 695, and 613 extend all the way to the upper surface 658 of the package substrate 656. The traces extend downwardly along the edge surfaces so that the bottom portion of each trace terminates at the bottom of the edge surface, where the traces join the conductive elements 663 on the upper surface of the package substrate.

In yet another variation, a carrier used to hold the traces and top terminals may be an element other than a sheet. For example, the traces and terminals can be deposited onto a mold element which is then used to form the top surface and edge surfaces of a dielectric mass. When the mold is removed, the top terminals and traces remain embedded in the dielectric mass, in much the same way as discussed with reference to FIGS. 1-10A above.

The packages discussed above can be utilized in construction of diverse electronic systems. For example, a system 900 (FIG. 22) in accordance with a further embodiment of the invention includes a first package 902 as described above in conjunction with a stack 904 incorporating two packages as described above, and in conjunction with other electronic components 908 and 910. In the example depicted, component 908 is a semiconductor chip whereas component 910 is a display screen, but any other components can be used. Of course, although only two additional components are depicted in FIG. 22 for clarity of illustration, the system may include any number of such components. Packages 902 and 904 and components 908 and 910 are mounted to a common housing 901, schematically depicted in broken lines, and are electrically interconnected with one another as necessary to form the desired circuit. In the exemplary system shown, the system includes a circuit panel 907 such as a flexible or rigid printed circuit board, and the circuit panel includes numerous conductors 909, of which only one is depicted in FIG. 22, interconnecting the components with one another. An off-board connector 911 connects component 910 to the circuit panel. However, this is merely exemplary; any suitable structure for making electrical connections can be used. The housing 901 is depicted as a portable housing of the type usable, for example, in a cellular telephone or personal digital assistant, and screen 910 is exposed at the surface of the housing. Again, the simplified system shown in FIG. 22 is merely exemplary; other systems, including systems commonly regarded as fixed structures, such as desktop computers, routers and the like can be made using the packages discussed above.

As these and other variations and combinations of the features discussed above can be utilized without departing from the present invention, the foregoing description of the preferred embodiments should be taken by way of illustration rather than by way of limitation of the invention as defined by the claims.

INDUSTRIAL APPLICABILITY

The present invention enjoys wide industrial applicability including, but not limited to, assemblies and methods for providing a package for a microelectronic element. 

I claim:
 1. A method of making a microelectronic package comprising the steps of: (a) positioning a sheet bearing a plurality of traces over an assemblage of a package substrate with conductive elements and a microelectronic element overlying the package substrate and electrically connected to the conductive elements so that portions of at least some of the traces extend over the microelectronic element; (b) introducing a flowable composition between the sheet and the package substrate and around the microelectronic element and curing the composition to form an overmold covering the microelectronic element and having a shape at least partially defined by the sheet; and (c) removing the sheet so as to leave the traces extending over one or more surfaces of the overmold facing away from the package substrate, wherein the step of positioning the sheet includes positioning a first portion of the sheet and first portions of the traces on the first portion of the sheet extending over the microelectronic element and positioning a second portion of the sheet so that the second portion of the sheet and second portions of the traces on the second portion of the sheet extend from the first portion of the sheet toward the package substrate.
 2. The method as claimed in claim 1 wherein the positioning step includes deforming the sheet.
 3. The method as claimed in claim 1 wherein the positioning step is performed so that a surface of the sheet bearing the traces faces toward the package substrate and the introducing step is performed so that the flowable composition partially surrounds the traces.
 4. The method as claimed in claim 3 wherein the sheet is formed from a metallic material and the step of removing the sheet includes etching the metallic material of the sheet.
 5. A method of making a microelectronic package comprising the steps of: (a) positioning a sheet bearing a plurality of traces over an assemblage of a package substrate with conductive elements and a microelectronic element overlying the package substrate and electrically connected to the conductive elements, the positioning step being performed so that a first portion of the sheet and first portions of the traces on the first portion of the sheet extend over the microelectronic element and a second portion of the sheet and second portions of the traces on the second portion of the sheet extend from the first portion toward the package substrate; (b) introducing a flowable composition between the sheet and the package substrate and around the microelectronic element; (c) curing the composition to form an overmold covering the microelectronic element and having a shape at least partially defined by the sheet; and (d) electrically connecting the second portions of the traces with the conductive elements of the package substrate.
 6. The method as claimed in claim 5 wherein the step of electrically connecting the second portions of the traces with the conductive elements is performed before the step of introducing the flowable composition.
 7. The method as claimed in claim 5 wherein the steps of positioning the sheet and introducing and curing the flowable composition are performed so that the overmold includes a main portion defining a top surface extending over the microelectronic element, a first edge surface bounding the main portion and extending downwardly toward the microelectronic element and a flange portion thinner than the main portion extending outwardly from the first edge surface, and so that the second portions of the traces include bottom portions extending over the flange portion, the step of electrically connecting the second portions including forming connections through the flange portion of the overmold.
 8. The method as claimed in claim 7 further comprising the step of forming vias in the flange portion of the overmold extending between the bottom portions of the traces and the package substrate, the step of forming connections through the flange portion including forming via conductors in the vias.
 9. The method as claimed in claim 8 wherein the step of forming vias in the flange portion of the overmold is performed after the steps of introducing and curing the composition.
 10. A method of making a microelectronic package comprising the steps of: (a) depositing a conformal dielectric layer onto an assemblage of a package substrate with conductive elements including bottom terminals exposed at a lower surface of the package substrate and a microelectronic element overlying an upper surface of the package substrate and electrically connected to the conductive elements, the depositing step being performed so that a first portion of the conformal layer defines a top surface remote from the package substrate and extending over the microelectronic element and one or more additional portions define one or more edge surfaces extending downwardly toward the package substrate outside of an area covered by the microelectronic element; and (b) providing traces and top terminals on the conformal layer so that the traces extend along the top surface and extend toward the package substrate along at least one edge surface and bottom portions of the traces are positioned adjacent the package substrate; and (c) connecting the bottom portions of the traces to at least some of the conductive elements on the package substrate, wherein the step of depositing a conformal layer is performed so that the conformal layer forms at least one upwardly-facing flange surface extending from a bottom border of at least one edge surface so that each flange surface is disposed at a vertical distance from the package substrate less than a vertical distance between the package substrate and the top surface, the step of providing traces is performed so that bottom portions of the traces extend over the at least one flange surface and the step of connecting the bottom portions of the traces includes forming connections so that the connections extend through the at least one flange surface.
 11. The method as claimed in claim 10 wherein the step of providing the traces and the terminals includes providing the traces and terminals on the conformal layer before depositing the layer onto the assemblage.
 12. The method as claimed in claim 11 wherein the step of providing the traces and the terminals includes depositing the traces onto the conformal layer after depositing the layer onto the assemblage. 